1. Field of the Invention
The present invention relates to a spinneret assembly capable of spinning sheath-core type composite fibers in which the ratio of core component to the sheath component is uniform from a single fiber to another and the core positions are constant.
2. Statement of the Prior Art
A number of spinneret assemblies for obtaining fibers of the sheath-core composite structure from two types of spinning stock solutions have heretofore been known in the prior art. Composite fibers have been spun out of a number of spinning holes open on a spinning plane of such spinneret assemblies. However, little or no attention has been paid to the elimination of ununiformity in the composite structure among fibers, which would result from the location of the spinning holes and the arrangement of the passages through which stock solutions are fed to the spinning holes. One example of such conventional spinneret assemblies is dislcosed in Japanese Patent Publication No. 62-37126, and will now be explained with reference to the drawings. FIG. 12 is a partly omitted, sectional view showing the conventional spinneret assembly, FIG. 13 is a plan view of a first distributor used in the assembly of FIG. 12, and FIG. 14 is a plan view of a second distributor used therein.
In the conventional spinneret assembly shown generally at 1, a stack of a spinneret plate 2, a second distributor 3, a first distributor 4, a filter 5 and a cap 6 are housed in that order from below within a casing 7, as illustrated in FIG. 12, with a gap 8 being provided between the spinneret plate 2 and the second distributor 3 along their full length. In an upper plane of the second-distributor 3, there are an alternate and parallel arrangement of core-component-stock-distributing-grooves 3a and sheath-component-stock-solution-distributing-grooves 3b, as illustrated in FIG. 14. The first-distributor 4 superposed on the second-distributor 3 (i.e., FIG. 13 being superposed on FIG. 14 as such and without changing direction) and shown in FIG. 13 includes core-component-stock-solution-inlet-holes 4a and sheath-component-stock-solution-inlet-holes 4b to which core- and sheath-component-stock-solutions are separately fed through the filter 5 for introduction into the distributing-grooves 3a and 3b in the second-distributor 3. The core- and sheath-component-stock-solutions introduced into the distributing-grooves 3a and 3b are guided to the gap 8 through the associated holes 3c and 3d for regulating the pressures of both component-stock-solutions respectively. In the gap 8, spinning holes 2a are open at positions coaxial with respect to the holes 3c for regulating the pressure of the core-component-stock-solution, so that the core-component-stock-solution is forced substantially straight into the spinning-holes 2a while is surrounded by the sheath-component-stock-solution, and spun out of the spinning plane. In the structure of such a spinneret assembly according to the prior art, the holes 3d for regulating the pressure of the sheath-component-stock-solution in the second-distributor 3 are located at the apexes of a rectangle, and the hole 3c for regulating the pressure of the core-component-stock-solution is located at the center of said rectangle, as shown by a dotted chain line in FIG. 14, whereby the distances of the sheath-component-stock-solution flowing in one spinning hole 2a from the holes 3d are designed to be equalized to make uniform the thickness of the sheath component surrounding the core component. In this respect, this structure is effective. However, even when the holes 3c and 3d and the spinning holes 2a are located as described above, there is a difference in the composite structures between the fiber spun out of the spinning holes 2a located at the ends and the fiber spun out of the holes at the center of the array of the spinning holes. That is, the sheath-component-stock-solution is uniformly fed to the central spinning hole 2a from its surrounding four holes 3d (in this case, one hole 3d serves to feed the stock solution to four spinning holes 2a), whereas a large amount of the sheath-component-stock-solution is fed to the endmost spinning hole 2a from two holes 3d (due to the fact that one hole 3d serves to feed the stock solution to one or two spinning holes 2a alone), so that the ratio of the sheath component to the core component in the composite structures spun out is larger in the endmost holes 2a than in the central hole 2a. In this case, not only is the sheath/core ratio different, but the core positions are also eccentric toward the sheath component being reduced. Even though the illustrated array of spinning holes 2a is changed to a circular one, the aforesaid disadvantage is unavoidable, as long as the construction of the passages for feeding the stock solutions is principally identical.